This question was put in the case of Clark and Clark & Ors . The two parties involved had regularly spent weekends at each other’s houses and travelled overseas together. However the parties did not have a permanent residence together.
The parties had a child in 2007 together. The father described the conception of their child as a “fling” The father said that the DVD of the wedding played to the court was a `mock wedding ceremony’ to ensure that people in their community would not attach “the stigma of illegitimacy” to their child.
However, Judge Burchardt said at  that it “sits…uneasily with the [father’s} assertion that the parties were not in a [de facto] relationship”, as did the other evidence at  of “something more than ordinary friendship” (including photographs, draft financial agreement, and a family Medicare card).
The court said that “….While there are clearly some indicia that would point against [the existence of a de facto relationship] such as the lack of permanent joint residence, the non-intermingling of bank accounts… and the fact of whatever relationship the applicant continued with [his former wife] these are all vastly outweighed by all the other numerous factors…”